U.S. patent application number 14/285037 was filed with the patent office on 2014-12-18 for projector.
This patent application is currently assigned to SEIKO EPSON CORPORATION. The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Nobuo SUGIYAMA.
Application Number | 20140368746 14/285037 |
Document ID | / |
Family ID | 52018936 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140368746 |
Kind Code |
A1 |
SUGIYAMA; Nobuo |
December 18, 2014 |
PROJECTOR
Abstract
A projector includes a lamp, a ballast, an aperture member
including light-blocking plates, a light-blocking plate driving
motor, a control section, a light modulation device, and a
projection optical system, and the control section controls the
ballast and the light-blocking plate driving motor so as to
modulate the lamp power based on a luminance of the video signal
while fixing the aperture of the aperture member to a constant
value in a picture period in accordance with a luminance parameter
corresponding to a video signal group in the picture period among a
series of the video signals.
Inventors: |
SUGIYAMA; Nobuo;
(Azumino-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
52018936 |
Appl. No.: |
14/285037 |
Filed: |
May 22, 2014 |
Current U.S.
Class: |
348/759 |
Current CPC
Class: |
H04N 9/3105 20130101;
H04N 9/3155 20130101; H04N 5/7416 20130101 |
Class at
Publication: |
348/759 |
International
Class: |
H04N 5/74 20060101
H04N005/74 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2013 |
JP |
2013-125325 |
Claims
1. A projector comprising: a light source adapted to emit light and
vary light intensity in accordance with a light source power
supplied to the light source; a light source power supply section
adapted to supply the light source with the light source power; an
aperture member having a variable aperture of a transmitting area
through which the light emitted from the light source is
transmitted; an aperture drive device adapted to drive the aperture
member to control the aperture; a control section adapted to
control the light source power supply section and the aperture
drive device; a light modulation device adapted to modulate the
light emitted from the light source based on a video signal; and a
projection optical system adapted to project the light modulated by
the light modulation device, wherein the control section controls
the light source power supply section and the aperture drive device
so as to modulate the light source power based on a luminance of
the video signal while fixing the aperture of the aperture member
to a constant value during a picture period in accordance with a
luminance parameter corresponding to a video signal group in the
picture period among a series of the video signals.
2. The projector according to claim 1, wherein one of the luminance
parameters is an average picture level in the picture period.
3. The projector according to claim 2, wherein the control section
determines the length of the picture period in accordance with the
average picture level.
4. The projector according to claim 1, wherein one of the luminance
parameters is a peak luminance value in the picture period.
5. The projector according to claim 4, wherein the control section
determines the aperture of the aperture member in accordance with
the peak luminance value.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a projector.
[0003] 2. Related Art
[0004] In the past, there has been known a projector as one of
display devices. The projector modulates light from, for example,
an illumination device with a light modulation device to thereby
form an image, and then projects the image on a screen with a
projection optical system. In the projector, there has been
proposed a technology for controlling the intensity of the light
emitted from a light source with a dimming device to thereby
improve the contrast of the image (see, e.g., JP-A-2010-243976
(Document 1) and JP-A-2010-211035 (Document 2)).
[0005] In the projectors of Document 1 and Document 2, the dimming
device is provided with a light-blocking member for blocking at
least a part of the light from the light source. The light-blocking
member moves into and out from a light path in between the light
source and a light modulation device. The intensity of the light to
be blocked by the light-blocking member out of the light from the
light source varies in accordance with the position of the
light-blocking member. As a result, according to the projector, the
intensity of the light entering the light modulation device can be
controlled.
[0006] As described above, the dimming device used in the
projectors of Document 1 and Document 2 is for mechanically driving
the light-blocking member to control an amount of the transmitted
light. However, since there is a limitation in the operation speed
of the light-blocking member, there is a problem that the
light-blocking member cannot sufficiently follow the change in
luminance, and thus correct dimming cannot be performed in the case
in which the rate of the change in luminance of the picture is
high. Further, there is a problem that the noise is increased in
the case in which the operation frequency of the light-blocking
member is raised in accordance with the change in luminance of the
picture.
SUMMARY
[0007] An advantage of some aspects of the invention is to provide
a projector capable of correct dimming following a change in
luminance of a picture, and of reducing a noise due to an operation
of a mechanical dimming device.
[0008] A projector according to an aspect of the invention includes
a light source adapted to emit light and vary light intensity in
accordance with a light source power supplied to the light source,
a light source power supply section adapted to supply the light
source with the light source power, an aperture member having a
variable aperture of a transmitting area through which the light
emitted from the light source is transmitted, an aperture drive
device adapted to drive the aperture member to control the
aperture, a control section adapted to control the light source
power supply section and the aperture drive device, a light
modulation device adapted to modulate the light emitted from the
light source based on a video signal, and a projection optical
system adapted to project the light modulated by the light
modulation device, and the control section controls the light
source power supply section and the aperture drive device so as to
modulate the light source power based on a luminance of the video
signal while fixing the aperture of the aperture member to a
constant value during a certain picture period in accordance with a
luminance parameter corresponding to a video signal group in the
picture period among a series of the video signals.
[0009] In other words, the projector according to the aspect of the
invention is provided with both of a mechanical dimming device
adapted to drive the aperture member to vary the aperture to
thereby control the amount of the transmitted light, and a light
source dimming device adapted to vary the light source power to
thereby control the amount of light emitted from the light source.
Therefore, the projector according to the aspect of the invention
easily follows the luminance variation of the picture compared to
the projector of the related art provided only with the mechanical
dimming device, and is capable of reducing the noise due to the
operation of the mechanical dimming device.
[0010] Further, in the projector according to the aspect of the
invention, the aperture of the aperture member is fixed to a
constant, value during a picture period in accordance with a
luminance parameter corresponding to the video signal group in the
picture period, and the light source power is varied to thereby
adjust the amount of the light emitted from the light source. Thus,
the followability with respect to the luminance variation of the
picture can be improved compared to the projector of the related
art, and the operation frequency of the mechanical dimming device
decreases, and thus the noise can be reduced.
[0011] One of the luminance parameters may be an average picture
level in the picture period. On this occasion, the control section
can also determine the length of the picture period in accordance
with the average picture level.
[0012] One of the luminance parameters may be a peak luminance
value in the picture period. On this occasion, the control section
can determine the aperture of the aperture member in accordance
with the peak luminance value. On this occasion, in order to make
the aperture of the aperture member correspond to the peak
luminance value in the picture period, the aperture of the aperture
member is maximized within a light amount control range in the
picture period. Therefore, in addition to the improvement, of the
followability to the luminance variation of the picture, and the
reduction of the noise, there can be obtained an advantage that the
amount of the light blocked by the aperture member can be reduced
to thereby reduce the heat load on the aperture member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0014] FIG. 1 is a schematic configuration diagram of a projector
according to an embodiment of the invention.
[0015] FIG. 2 is a flowchart for explaining an operation of a
control section.
[0016] FIG. 3 is a diagram for explaining a dimming method of the
projector according to the embodiment.
[0017] FIG. 4 is a diagram for explaining a dimming method of a
projector according to an comparative example.
[0018] FIG. 5 is a diagram for explaining an operation amount of a
mechanical dimming device in the projector according to the
embodiment.
[0019] FIG. 6 is a diagram for explaining an operation amount of a
mechanical dimming device in the projector according to the
comparative example.
DESCRIPTION OF AN EXEMPLARY EMBODIMENT
[0020] Hereinafter, an embodiment of the invention will be
explained with reference to the accompanying drawings.
[0021] The projector according to the present embodiment is an
example of a projector provided with three sets of liquid crystal
light valves as a light modulation device, namely a so-called
three-chip liquid crystal display (3LCD) projector.
[0022] In the following drawings, the constituents might be shown
with the respective scale ratios of the sizes different from each
other in order to make the constituents eye-friendly.
[0023] As shown in FIG. 1, the projector 1 according to the present
embodiment is provided with an optical unit 2, an exhaust fan 3, a
control section 4, and a housing 6. The control section 4 controls
a ballast 13 and a light-blocking plate driving motor 14 described
later. The optical unit 2 is provided with an illumination device
8, a color separation optical system 53, a light modulation device
55, a color combining optical element 554, and a projection optical
system 56. The illumination device 8 is provided with a light
source device 51 and a uniform illumination optical system 52.
[0024] Hereinafter, the optical unit 2 will be explained.
[0025] The light source device 51 emits light toward the uniform
illumination optical system 52. The light source device 51 is
provided with a light source main body 51A, a collimating lens 513,
and a housing member 514. The light source device main body 51A is
provided with a lamp 511, and a reflector 512. The lamp 511, the
reflector 512, and the collimating lens 513 are housed inside the
housing member 514. The reference symbol "A" in FIG. 1 denotes a
center axis of the light emitted from the lamp 511, which is
referred to as an illumination light axis in the following
explanation.
[0026] The lamp 511 has an emission center in the vicinity of a
primary focal point of the reflector 512. The lamp 511 has a bulb
section and a pair of sealing sections. The pair of sealing
sections extend on both sides of the bulb section. The bulb section
is formed of a spherical body made of quartz glass. The bulb
section has a pair of electrodes disposed inside the spherical
body, mercury, a noble gas, and a small amount of halogen
encapsulated in the spherical body. As the lamp 511, there can be
adopted, for example, a ultrahigh pressure mercury lamp, a
high-pressure mercury lamp, or a metal halide lamp. The reflector
512 has a cylindrical neck-like portion and a reflecting surface.
One of the sealing sections of the lamp 511 is inserted in and
fixed to the neck-like portion. The reflecting surface reflects the
light, which proceeds toward the reflector 512 out of the light
emitted from the lamp 511, toward the secondary focal position of
the reflector 512.
[0027] The lamp 511 varies in amount of emitted light in accordance
with the lamp power supplied. The ballast 13 is connected to the
lamp 511. The ballast 13 generates the lamp power in response to a
signal from the control section 4, and supplies the lamp 511 with
the lamp power. The ballast 13 corresponds to a "light source power
supply section" in the appended claims.
[0028] The uniform illumination optical system 52 is an optical
system for roughly uniformly illuminating an image forming area of
each of the liquid crystal light valves 551 with the light emitted
from the light source device 51. The uniform illumination optical
system 52 is provided with a first lens array 521, a second lens
array 522, a polarization conversion element 523, and an
superimposed lens 524.
[0029] The first lens array 521 has a configuration of arranging a
plurality of small lenses in a plane perpendicular to the
illumination light axis A in a matrix with a plurality of rows and
a plurality of columns. The first lens array 521 has a function as
a light beam dividing optical element for dividing the light
emitted from the collimating lens 513 into a plurality of partial
light beams. Although the explanation using the graphical
description is omitted, an outer shape of each of the small lenses
is similar to an outer shape of the image forming area of each of
the liquid crystal light valves 551.
[0030] Similarly to the first lens array 521, the second lens array
522 has a configuration of arranging a plurality of small lenses in
a plane perpendicular to the illumination light axis A in a matrix
with a plurality of rows and a plurality of columns. The second
lens array 522, in conjunction with the superimposed lens 524, has
a function of focusing the image of the small lenses of the first
lens array 521 in the vicinity of the image forming area of each of
the liquid crystal light valves 551.
[0031] The polarization conversion element 523 converts each of the
partial beams divided into by the first lens array 521 into a
substantially unique linearly-polarized light beam having a uniform
polarization direction, and then emits the resulted partial light
beams. The polarization conversion element 523 has a polarization
separation layer, a reflecting layer, and a wave plate. The
polarization separation layer transmits one polarized light (e.g.,
P-polarized light) out of the illumination light from the lamp 511,
and reflects the other polarized light (e.g., S-polarized light)
toward a direction perpendicular to the illumination light axis A.
Further, the reflecting layer reflects the light having the other
polarized light, which has been reflected by the polarization
separation layer, in a direction parallel to the illumination light
axis A. The wave plate converts the light having the one polarized
light having been transmitted through the polarization separation
layer into the light having the other polarized light.
[0032] The superimposed lens 524 is an optical element for
collecting the plurality of partial light, beams having passed
through the first lens array 521, the second lens array 522, and
the polarization conversion element 523 to overlap them in the
vicinity of the image forming area of each of the liquid crystal
light valves 551. The superimposed lens 524 is disposed so that the
optical axis of the superimposed lens 524 and the illumination
light axis A of the illumination device 8 roughly coincide with
each other. The superimposed lens 524 can also be formed of a
compound lens having a plurality of lenses combined with each
other.
[0033] An aperture member 16 is disposed between the first lens
array 521 and the second lens array 522 as the constituents of the
uniform illumination optical system 52. The aperture member 16 is
provided with, for example, a pair of light-blocking plates 17 each
arranged to be rotatable around a rotation axis. The size
(aperture) of an opening AP between the pair of light-blocking
plates 17 varies due to the rotation of the pair of light-blocking
plates 17. Thus, the aperture member 16 can control the amount of
transmission of the light emitted from the light source device 51.
It should be noted that it is also possible to use an iris-type
aperture member provided with, for example, a plurality of aperture
blades instead of the aperture member 16 having the pair of
light-blocking plates 17, and the type of the aperture member is
not particularly limited.
[0034] The light-blocking plate driving motor 14 for driving the
pair of light-blocking plates 17 is connected to the aperture
member 16. As the light-blocking plate driving motor 14, there can
be used, for example, a voice coil motor or a stepping motor. The
light-blocking plate driving motor 14 drives the pair of
light-blocking plates 17 in response to a signal from the control
section 4 to control the aperture of the opening AP. The
light-blocking plate driving motor 14 corresponds to an "aperture
drive device" in the appended claims.
[0035] The color separation optical system 53 is provided with a
first dichroic mirror 531, a second dichroic mirror 532, and a
reflecting mirror 533. The first dichroic mirror 531 and the second
dichroic mirror 532 have a function of separating the plurality of
partial light beams emitted from the uniform illumination optical
system 52 into colored light beams of the three colors of red (R),
green (G), and blue (B). The first dichroic mirror 531 transmits
the red light and the green light, and reflects the blue light. The
second dichroic mirror 532 transmits the red light among the
colored light beams having been transmitted through the first
dichroic mirror 531, and reflects the green light.
[0036] In the first dichroic mirror 531, the red light and the
green light are separated from the blue light. The blue light is
reflected by the reflecting mirror 533, and is guided to the
blue-light liquid crystal light valve 551B. In the second dichroic
mirror 532, the green light and the red light are separated from
each other. The green light is guided to the green-light liquid
crystal light valve 551G. The color separation optical system 53 is
further provided with a relay optical device 54. The relay optical
device 54 is provided with an entrance side lens 541, relay lenses
543, a reflecting mirror 542, and a reflecting mirror 544. The
relay optical device 54 has a function of guiding the red light,
which has been separated into by the color separation optical
system 53, to the red-light liquid crystal light valve 551R in
order to prevent a loss of the red light longer in light path than
other colored light beams. Field lenses 525 each convert each of
the partial light beams emitted from the second lens array 522 into
a light beam parallel to the center axis (the principal ray)
thereof.
[0037] The light modulation device 55 is provided with three liquid
crystal light valves 551 (the red-light liquid crystal light valve
551R, the green-light liquid crystal light valve 551G, and the
blue-light liquid crystal light valve 551B), entrance side
polarization plates 552 and exit side polarization plates 553
respectively disposed on the light entrance side and the light exit
side of the liquid crystal light valves 551. The light modulation
device 55 modulates the light, which has been emitted from the
illumination device 8 and has entered the light modulation device
55, based on the image signal.
[0038] The color combining optical element 554 is formed of a cross
dichroic prism. The color combining optical element 554 combines
the light beams having been modulated by the liquid crystal light
valves 551 of the respective colors. The cross dichroic prism is an
optical element for combining the respective colored light beams to
form a color image. The cross dichroic prism has a roughly square
shape in the plan view formed by bonding four rectangular prisms to
each other. On the boundary surfaces having a roughly X shape on
which the rectangular prisms are bonded to each other, there are
formed dielectric multilayer films. The dielectric multilayer film
formed on one of the roughly X-shaped boundary surfaces reflects
the blue light, and the dielectric multilayer film formed on the
other of the boundary surfaces reflects the red light. The blue
light and the red light are respectively deflected by these
dielectric multilayer films to have the proceeding direction
aligned with the proceeding direction of the green light, and thus
the three colored light beams are combined.
[0039] Although not shown in the drawings, the projection optical
system 56 includes a plurality of projection lenses, which the
light having been combined by the color combining optical element
554 enters, and a projection lens housing for housing the plurality
of projection lenses.
[0040] The illumination light axis A of the illumination device 8
and a projection optical, axis B of the projection optical system
56 are perpendicular to each other. The exhaust fan 3 is disposed
in an area surrounded by the illumination device 8 and the
projection optical system 56. The exhaust fan 3 is formed of, for
example, a sirocco fan. An exhaust port 10 is disposed on the
lateral side of the projection optical system 56 among the side
surfaces of a lower case 11. The exhaust fan 3 discharges a
high-temperature air existing inside the housing 6 to the outside
through the exhaust port 10. The flow of the hot air is indicated
by the arrow denoted with the symbol FE.
[0041] The control section 4 controls the ballast 13 and the
light-blocking plate driving motor 14. In the control section 4, a
video signal SG input thereto is temporarily stored in a frame
memory 19 via a buffer 18. The frame memory 19 preferably has a
capacity capable of storing as much video signals as possible. In
the present embodiment, the frame memory 19 has a capacity capable
of storing at least the video signals SG corresponding to one
picture period (e.g., 2 seconds) described later. Besides the
above, the control section 4 controls the light modulation device
55 in response to the video signal SG. It should be noted that in
the present embodiment, the control of the light modulation device
55 is general, and will therefore be omitted from the
explanation.
[0042] The projector 1 according to the present embodiment is
provided with dimming devices for the purpose of improving the
contrast of an image. One of the dimming devices is for controlling
the amount of the transmitted light using the aperture member 16
after the light is emitted from the light source device 51. The
aperture member 16 has a configuration of mechanically driving the
pair of light-blocking plates 17 using the light-blocking plate
driving motor 14, and is therefore hereinafter referred to as a
mechanical dimming device. The other of the dimming devices is for
controlling the ballast 13 to vary the lamp power to thereby
control, the emitted light amount of the lamp 511 itself, and is
hereinafter referred to as a lamp dimming device.
[0043] In the projectors of the related art provided only with the
mechanical dimming device, there are a problem of a poor
followability of the mechanical dimming device and a problem of a
noise due to the operation of the mechanical dimming device. In
contrast, in the projector 1 according to the present embodiment,
since both of the mechanical dimming device and the lamp dimming
device are provided, the followability of the whole of the dimming
devices is improved, and the noise can be reduced.
[0044] Here, in the projector, in the case of providing both of the
mechanical dimming device and the lamp dimming device, the
following method can be adopted as the control method of these two
types of dimming devices. The control method explained below is a
comparative example.
[0045] FIG. 4 is a diagram for explaining the control method of the
comparative example, wherein the horizontal axis of the graph
represents the time (minute), and the vertical axis represents the
luminance value of the video signal. The luminance value is an
index representing brightness of the picture in each of the video
signals, and can be thought to be, for example, a gray level of the
video signal. In FIG. 4, there is shown a variation in the
luminance value of the video signal in a certain period, wherein
the maximum luminance value is 200 and the minimum luminance value
is 62. Hereinafter, the explanation is continued using the rate of
each of the luminance values assuming that the maximum luminance
value of 200 corresponds to 100% as a light control rate.
[0046] In the method of the comparative example, the lamp dimming
device is made function in a range of the light control rate of 80%
through 100%, and the mechanical dimming device is made function in
a range of the light control rate of 30% through 80%. The reason
that the lamp dimming device is used on the side where the light
control rate is high is that the reliability of the lamp cannot be
ensured on the side where the light control rate is low, namely the
side where the amount of the light is significantly reduced. In
other words, in the method of the comparative example, the region
the lamp dimming device is in charge of and the region the
mechanical dimming device is in charge of are separated from each
other depending on the value of the light control rate.
[0047] In FIG. 4, the lamp dimming device deals with the dimming in
a range above the straight line A, and the mechanical dimming
device deals with the dimming in a range below the straight line A.
For example, in the period of t.sub.1 through t.sub.2, the lamp
dimming device is in charge of roughly the entire period, and in
the period of t.sub.3 through t.sub.4, the mechanical dimming
device is in charge of roughly the entire period. In this example,
in the range below the straight line A, the mechanical dimming
device is made to deal with the luminance variation while fixing
the light control rate due to the lamp dimming device to 30%.
However, it is difficult for the mechanical dimming device to
accurately follow such a rapid luminance variation. Further, it
results that the mechanical dimming device always operates during
the period with the light control rate not higher than 80%, and the
noise continuously occurs.
[0048] In contrast, the control method of the dimming devices
according to the present embodiment is a method of modulating the
lamp power based on the luminance of the video signal SG in the
state in which the aperture of the aperture member 16 is fixed to a
certain value in a certain picture period in accordance with a
luminance parameter corresponding to a video signal group in the
picture period among the series of video signals.
[0049] FIG. 2 is a flowchart showing the control method according
to the present embodiment. FIG. 3 is a diagram for explaining the
control method according to the present embodiment, and the content
of FIG. 3 is roughly the same as the content of FIG. 4.
[0050] In the control method of the dimming devices according to
the present embodiment, the control section 4 firstly acquires
(step S1 in FIG. 2) the video signals in a certain period into the
frame memory 19 via the buffer 18. The capacity of the frame memory
is preferably as high as possible, and is preferably capable of
acquiring the video signals SG corresponding to, for example, about
several seconds through 10 seconds.
[0051] Then, assuming that the frame memory 19 is capable of
acquiring the video signals for 10 seconds, the control section 4
obtains an average picture level (hereinafter abbreviated as APL)
of the series of video signals SG as the luminance parameter. In
the example shown in FIG. 3, the series of video signals SG is
categorized into five video signal groups, namely a video signal
group with the APL of 180 (the light control rate of 90%), a video
signal group with the APL of 160 (the light control rate of 80%), a
video signal group with the APL of 1.10 (the light control rate of
55%), a video signal group with the APL of 180 (the light control
rate of 90%), and a video signal group with the APL of 120 (the
light control rate of 60%) in chronological order.
[0052] A period corresponding to one video signal group is referred
to as a picture period. The picture periods corresponding to the
five video signal groups are referred to as a first picture period,
a second picture period, a third picture period, a fourth picture
period, and a fifth picture period, respectively, in chronological
order. These picture periods can be determined based on the
APL.
[0053] Further, the control section 4 obtains (step S2 in FIG. 2)
the peak luminance values P1 through P5 in the respective picture
periods as the luminance parameter. In the example shown in FIG. 3,
the peak luminance value P1 in the first picture period becomes 190
(the light control rate of 95%), the peak luminance value P2 in the
second picture period becomes 190 (the light control rate of 95%),
the peak luminance value P3 in the third picture period becomes 150
(the light control rate of 75%), the peak luminance value P4 in the
fourth picture period becomes 200 (the light control rate of 100%),
and the peak luminance value P5 in the fifth picture period becomes
180 (the light control rate of 90%).
[0054] Subsequently, the control section 4 determines (step S3 in
FIG. 2) the aperture of the light-blocking plates 17 in the
aperture member 16 based on the peak luminance values P1 through P5
in the respective picture periods obtained in the step S2. On this
occasion, the control section 4 applies the light control rate of
each of the peak luminance values P1 through P5 in the respective
picture periods directly to the aperture of the light-blocking
plates 17. Specifically, the aperture of the light-blocking plates
17 in the first picture period is set to 95%, the aperture of the
light-blocking plates 17 in the second picture period is set to
95%, the aperture of the light-blocking plates 17 in the third
picture period is set to 75%, the aperture of the light-blocking
plates 17 in the fourth picture period is set to 100%, and the
aperture of the light-blocking plates 17 in the fifth picture
period is set to 90%. For example, since the peak luminance value
does not vary between the first picture period and the second
picture period, the aperture of the light-blocking plates 17 is not
varied.
[0055] The control section 4 controls the light-blocking plate
driving motor 14 in accordance with the aperture of the
light-blocking plates 17 to adjust the light-blocking plates 17 so
as to have the given aperture. On this occasion, in each of the
picture periods, the aperture of the light-blocking plates 17 is
fixed to a constant value without following the luminance
variation.
[0056] Subsequently, the control section 4 determines (step S4 in
FIG. 2) the lamp power to be supplied to the lamp 511 in accordance
with the luminance variation of the video signal group in each of
the picture periods. Specifically, the control section 4 stores a
look-up table (LUT) showing a relationship between the luminance
value and the ballast output signal corresponding to the lamp power
using the aperture of the light-blocking plates 17 as a parameter.
The control section 4 reads out an instruction signal, which
corresponds to the luminance value, and is provided to the ballast
13, from the LUT, and then outputs the instruction signal to the
ballast 13. The ballast 13 outputs the lamp power, which is based
on the instruction signal thus input, to the lamp 511.
[0057] The light control rate of the lamp 511 is preferably set to
a value within a range where the reliability of the lamp 511 is not
impaired. The light control rate of the lamp 511 is preferably set
in a range of, for example, 50 through 100%, and is more preferably
set in a range of 70 through 100%. It should be noted that even in
the case of setting the light control rate of the lamp to a value
lower than 50%, there is no particular problem providing the period
in which the light control rate is lower than 50% is limited to a
rather short period. In the example shown in FIG. 3, the light
control rate of the lamp 511 is varied within a range of 90 through
100% in the first picture period, the light control rate of the
lamp 511 is varied within a range of 70 through 100% in the second
picture period, the light control rate of the lamp 511 is varied
within a range of 60 through 100% in the third picture period, the
light control rate of the lamp 511 is varied within a range of 80
through 100% in the fourth picture period, and the light control
rate of the lamp 511 is varied within a range of 40 through 100% in
the fifth picture period.
[0058] Here, an amount of movement of the light-blocking plates 17,
namely the variation in aperture of the light-blocking plates 17
from the aperture in the present picture period to the aperture in
the subsequent picture period, is compared between the control
method according to the comparative example and the control method
according to the present embodiment.
[0059] In the comparative example, as shown in FIG. 6, since the
mechanical dimming device is in charge of the region with the
luminance value lower than 180 (the light control rate of 80%), the
point with the luminance value of 180 (the light control rate of
80%) is made to correspond to the aperture of 100%. Further, here,
for the sake of convenience of calculation, it is assumed that the
light-blocking plates 17 are not driven precisely in accordance
with each of the luminance values, but are driven so as to match
the APL in each of the picture periods shown in FIG. 5. On this
occasion, the aperture of the light-blocking plates in the first
picture period becomes 100%, the aperture of the light-blocking
plates in the second picture period becomes 94%, the aperture of
the light-blocking plates in the third picture period becomes 69%,
the aperture of the light-blocking plates in the fourth picture
period becomes 100%, and the aperture of the light-blocking plates
in the fifth picture period becomes 75%.
[0060] In the control method according to the comparative example
and the control method according to the present embodiment, the
aperture of the light-blocking plates 17 in each of the picture
periods, an operation width of the light-blocking plates 17 from
the previous picture period to the present picture period, and a
difference in operation width between the present embodiment and
the comparative example are organized as Table 1 below.
TABLE-US-00001 TABLE 1 Difference Comparative Present between
Example Embodiment present Aperture Aperture embodiment of light-
of light- and Picture blocking Operation blocking Operation
comparative period plates width plates width example First 100% --
95% -- -- picture period Second 64% 6% 95% 0% -6% picture period
Third 69% 25% 75% 20% -5% picture period Fourth 100% 31% 100% 25%
-6% picture period Fifth 75% 25% 90% 10% -15% picture period
[0061] As shown in Table 1, in the comparative example, the
operation width of the light-blocking plates from the first picture
period to the second picture period is 6%, the operation width of
the light-blocking plates from the second picture period to the
third picture period is 25%, the operation width of the
light-blocking plates from the third picture period to the fourth
picture period is 31%, and the operation width of the
light-blocking plates from the fourth picture period to the fifth
picture period is 25%. In contrast, in the present embodiment, the
operation width of the light-blocking plates from the first picture
period to the second picture period is 0%, the operation width of
the light-blocking plates from the second picture period to the
third picture period is 20%, the operation width of the
light-blocking plates from the third picture period to the fourth
picture period is 25%, and the operation width of the
light-blocking plates from the fourth picture period to the fifth
picture period is 10%. As described above, it has been found out
the fact that according to the control method of the present
embodiment, the operation width of the light-blocking plates 17 can
be reduced 5 through 15% compared to the control method according
to the comparative example.
[0062] In the case, for example, of using a voice coil motor (VCM)
as the light-blocking plate driving motor 14, the operation time of
the voice coil motor necessary to change the aperture from 0% to
100% is about 0.1 second. In the case in which the maximum
operation width of the light-blocking plates 17 is 25% as in the
present embodiment, the operation time becomes 0.025 second, which
shows that the voice coil motor can be used without a problem. In
contrast, in the case of using a stepping motor (SM), the operation
time of the stepping motor necessary to change the aperture from 0%
to 100% is about 1 second. As described above, the stepping motor
is low in response speed compared to the voice coil motor, and is
therefore difficult to use as the light-blocking plate driving
motor 14. It should be noted that in the case in which the maximum
operation width of the light-blocking plates 17 is 25%, the
operation time of the stepping motor becomes 0.25 second, which is
a level allowing the use of the stepping motor.
[0063] Then, the operation rate of the light-blocking plates 17 is
compared between the control method according to the comparative
example and the control method according to the present
embodiment.
[0064] Assuming that the operation time of the voice coil motor is
0.025 second and the operation time of the stepping motor is 0.25
second in the case in which the operation width of the
light-blocking plates 17 is 25% as described above, and the length
of one picture period is 2 seconds, the operation rate can be
calculated as Table 2 below.
TABLE-US-00002 TABLE 2 Type of Comparative Present light-blocking
Example Embodiment plate driving Operation Operation Operation
motor time Followability rate Followability rate Voice coil motor
0.025 sec A 100% A 1.25% Stepping motor 0.25 sec C 100% B 12.5%
[0065] In Table 2, the symbol "A" represents sufficiently good
followability, the symbol "B" represents good followability, and
the symbol "C" represents poor followability.
[0066] As shown in Table 2, in the comparative example, since the
light-blocking plates are always operating during the picture
period the mechanical dimming device is in charge of, the operation
rate is 100% irrespective of the type of the motor. In contrast, in
the present embodiment, it is possible to dramatically improve the
operation rate of the light-blocking plates 17 in one picture
period (2 seconds) to 1.25% with the voice coil motor, or to 12.5%
with the stepping motor.
[0067] According to the results described above, in the case of the
present embodiment, the voice coil motor can provide sufficient
followability as the light-blocking plate driving motor 14. In
contrast, the stepping motor cannot be used in the control method
according to the comparative example from the viewpoint of the
followability, but can be used in the control method according to
the present embodiment although inferior to the voice coil motor in
terms of the followability.
[0068] As described hereinabove, in the projector 1 according to
the present embodiment, the aperture of the aperture member 16 is
fixed to a constant value during each of the first through fifth
picture periods each corresponding to the group of the video
signals having a roughly equivalent APL, but is not varied
continuously in accordance with each of the video signals. On that
basis, in the projector 1 according to the present embodiment, the
lamp power is varied during the picture period to thereby control
the amount of the light emitted from the light source device 51 to
perform the dimming. In general, the lamp dimming is sufficiently
high in response speed compared to the mechanical dimming.
Therefore, in the projector 1 according to the present embodiment,
the followability with respect to the luminance variation of the
picture is improved compared to the projector of the related art.
Further, the operation width of the light-blocking plates 17 can be
reduced, and in addition, the operation rate of the light-blocking
plate 17, in other words, the operation frequency of the
light-blocking plates, can be lowered. Therefore, the noise can be
reduced.
[0069] In particular in the case of the present embodiment, since
the aperture of the light-blocking plates 17 is set in accordance
with the peak luminance value in each of the picture periods, there
is created a state in which the light-blocking plates 17 are opened
as widely as possible within a range in which the dimming devices
are capable of dealing with the luminance value of each of the
video signals. Then, the lamp dimming device controls the amount of
the light emitted from the lamp 511 in the dimming direction from
the maximum value (100%). Therefore, there is achieved the control
method in which the amount of the light blocked by the
light-blocking plates 17 is the smallest, and the heat load applied
to the light-blocking plates 17 becomes sufficiently small. As a
result, the reliability of the light-blocking plates 17 as the
mechanical dimming device can be improved.
[0070] It should be noted that the scope of the invention is not
limited to the embodiment described above, but various
modifications can be provided thereon within the scope or the
spirit of the invention.
[0071] For example, although in the embodiment described above, the
aperture of the aperture member is fixed in accordance with the
peak luminance value in each of the picture periods, it is also
possible to adopt a method of fixing the aperture of the aperture
member in accordance with, for example, the APL in each of the
picture periods, and then increasing or decreasing the amount of
the light emitted from the lamp using the lamp dimming device
instead of the method described above. Although in this method,
there is a possibility that the amount of the light blocked by the
light-blocking plates increases compared to the method of the
embodiment described above, and the heat load applied to the
light-blocking plates increases, it is sufficient to arbitrarily
adjust the aperture within the allowable range of the heat
load.
[0072] Besides the above, the specific configuration of each of the
constituents of the projector can arbitrarily be modified.
[0073] The entire disclosure of Japanese Patent Application No.
2013-125325, filed Jun. 14, 2013 is expressly incorporated by
reference herein.
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